SummaryIn 38 patients presenting Vaquez's disease, the erythropoïcsis was investigated by "Fe for the study of the fcrrokinctics and5lCr for the evaluation of red cell survival.These patients were classified in 3 groups :1)before any treatment with12P,2)during relapse after treatment.3)in clinical remission of polycythemia.In 13 patients, the modifications due to the treatment were evaluated bv multiple investigations.The study of blood and red cell volumes and of the various parameters of the ferrokinetics at different stages of the disease indicates the abnormalities of erythropoi'esis which characterize the evolution of polycythemia vera, and the influence of the treatment.The total red cell volume decreases before the red cell count. The59Fc half-life in plasma is increased bv the treatment with "P. When this is effective, the turn-over of plasmatic and erythrocytic iron decrease.The red cell survival is normal when the disease is of recent onset and is not modified by32P administration.The evolution of the disease and the consequences of the treatment can also be evaluate;! by external touting at the level of the sacrum, liver and spleen.The difference between erythrocytic iron turn-over and the amount of iron necessary for red cell replacement is accounted for bv an ineffective crvthropoic-sis which is observed at the different stages of the disease as well as during the remissions.These investigations indicate the interest of ferrokinetic studies during32P treatment in order to foresee the beginning of any remission or relapse of the disease.